The present-day extension of human lifespan comes at the cost of increased prevalence of aging-associated cardiovascular diseases (Lakatta E C. Age-associated cardiovascular changes in health: impact on cardiovascular disease in older persons. Heart Fail Rev. 2002; 7:29-49). One particular condition with high mortality is aortic aneurysm formation and subsequent rupture of the aortic vessel. Aortic aneurysm (AA) is a typical age-associated disease that affects approximately 9% of elderly men and leads to a significant number of death (Singh K, Bonaa K H, Jacobsen B K, Bjork L, Solberg S. Prevalence of and Risk Factors for Abdominal Aortic Aneurysms in a Population-based Study: The Tromso Study. Am J. Epidemiol. 2001; 154:236-244).
The incidence of AA is still increasing indicating that current primary preventive health care strategies e.g. by targeting blood pressure are not sufficiently effective in reducing AA. Surgery is currently the state-of-the-art treatment; however, this surgical intervention is associated with a significant morbidity and mortality, e.g. only 10-25% of patients survive rupture due to large pre-and post-operative mortality. On a mechanistic level, analysis of human pathological sections revealed that AA formation and rupture are characterized by thinning of the vascular wall. Decreased formation or destruction of extracellular matrix are believed to be the key pathophysiological processes leading to vascular wall thinning (Guo D C, Papke C L, He R, Milewicz D M. Pathogenesis of thoracic and abdominal aortic aneurysms. Ann N Y Acad Sci. 2006; 1085:339-352).
MicroRNAs (miRNAs) have recently emerged as key regulators of several (patho-) physiological processes miRNAs are short non-coding RNAs that regulate protein expression post-transcriptionally by inducing degradation of the targeted mRNA or by blocking protein translation. miRNAs are expressed as precursor transcripts which fold into a stem-loop structure. Precursor miRNAs are sequentially digested via the Drosha and Dicer nucleases to yield the mature miRNA duplex, which is then introduced into the miRNA associated RNA induced silencing complex (RISC). However, only one strand of the mature miRNA is retained in the complex and will provide the binding to the targeted mRNA. The target-sequence regions within the silenced gene transcript are mostly found in the untranslated regions of the respective mRNA; miRNAs bind preferably in the 3′ untranslated region of their target mRNA and facilitate translational inhibition or mRNA degradation.
Whereas various studies showed that specific miRNAs control vessel growth and cardiac function (Urbich C, Kuehbacher A, Dimmeler S. Role of microRNAs in vascular diseases; inflammation, and angiogenesis. Cardiovasc Res. 2008; 79:581-588), the involvement of miRNAs in AA formation and atherosclerotic plaque rupture and the impact of age on the expression of vascular miRNAs is unknown.
The microRNA family around miRNA-29 is known as a key regulator of fibrosis in cardiac tissue. WO 2009/018493 shows that members of the miRNA-29 family, miRNA-29a, b and c, are down-regulated in the heart tissue in response to stress, and are up-regulated in heart tissue of mice that are resistant to both stress and fibrosis. Aortic aneurysm formation is, however, not disclosed in WO 2009/018493.
Similarly, WO 2008/042231 discloses the therapeutic implications of miRNA expression in diseases of the heart. The altered miRNA expression in cardiomyocytes was found to elicit broad effects on the transcription of various genes in heart failure. For example, miR-1 regulates calmodulin expression levels. Predicted miR-1 targets include several that could contribute to heart failure pathogenesis; among these are Calm 1 and Calm 2, the primary calmodulin isoforms in the heart. The application suggests using miRNAs specifically expressed in affected heart tissue as therapeutic targets.
WO 2009/018493 discloses the use of miR-29a-c antagonists as profibrotic agents to convert soft plaques in the vasculature into fibrotic tissue to prevent myocardial infarction.
Several other MicroRNAs are key regulators in the onset of heart diseases. Silvestri et al. review that MiR-29 is involved in fibrotic reaction after myocardial infarction while miR-21 may exert a fundamental role in post-angioplasty restenosis. MiR-208 is involved in the shift toward a fetal gene expression pattern in contractile proteins in heart failure. MiR-1 influences susceptibility to cardiac arrhythmias after myocardial infarction (Silvestri P et al., MicroRNAs and ischemic heart disease: towards a better comprehension of pathogenesis, new diagnostic tools and new therapeutic targets. Recent Pat Cardiovasc Drug Discov. 2009 June; 4(2):109-18).
The expression of miRNA-29 in myocardial infarction is the starting point of a study about the protective effects of Pioglitazone (a PPAR-gamma agonist) against myocardial ischemia-reperfusion injury miRNA-29a and miRNA-29c were significantly less expressed after Pioglitazone administration to rats. Interestingly, Antagomirs of miRNA-29a and miRNA-29c significantly reduced myocardial infarct size and apoptosis in hearts subjected to IR injury. This was probably due to an increased expression of anti apoptotic factors (Mcl-2) in the heart (Ye Y, et al., Down-regulation of microRNA-29 by antisense inhibitors and a PPAR-{gamma} agonist protects against myocardial ischemia-reperfusion injury, Cardiovasc Res. 2010 Feb. 17). Furthermore, Golledge et al. (in Golledge J, et al. Peroxisome proliferator-activated receptor ligands reduce aortic dilatation in a mouse model of aortic aneurysm. Atherosclerosis. 2010 May; 210(1):51-6. Epub 2009 Oct. 29.) disclose that osteopontin is associated with human abdominal aortic aneurysms (AAA) and that in vitro studies suggest that this cytokine is downregulated by peroxisome proliferator-activated receptor (PPAR) ligation. Similarly, Jones et al. (in Jones A, et al. Rosiglitazone reduces the development and rupture of experimental aortic aneurysms. Circulation. 2009 Jun. 23; 119(24):3125-32. Epub 2009 Jun. 8.) discloses that rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, reduces aneurysm expansion or rupture. Pretreatment or posttreatment with rosiglitazone reduced aortic expansion and rupture in a mouse model. Reduction of lesions in animals pretreated with rosiglitazone is concomitant with decreased expression of inflammatory mediators. Further studies are described to be needed to elucidate the precise mechanism. Nevertheless, in these publications the effect of the ligands or rosiglitazone or pioglitazone are completely independent from the mechanisms involved in the present invention.
While no drug treatment at all has been approved and is available for a treatment of aortic aneurysm formation, risk factor modifications, as well as preventive therapy using statins and ACE-inhibitors have reduced the mortality due to atherosclerosis during the last 15 years. Most importantly, however, due to the increase in life expectancy and the increased age of the overall population, age-associated diseases like aneurysm formation are expected to further increase over time. Therefore, an efficient treatment is desperately needed. Current attempts to therapeutically interfere with abnormal vessel remodeling exclusively focus on taming the inflammatory response associated with alterations of vascular wall structures. However, there are no therapeutic options at all to modify the structural weakness of the vessel wall. Specific interventions blocking collagen-degrading proteinases or antibody-directed inhibition of recruitment of inflammatory cells turned out to be unsuccessful.